1. Field of the Invention
The present invention relates to the preparation of an alkoxylation catalyst and to a process of alkoxylation using the catalyst.
2. Description of Related Art
Alkylene oxide adducts of compounds containing “active” or “labile” hydrogens find utility in a variety of products such as, for example, surfactants, solvents, and chemical intermediates. Typically, these alkylene oxide adducts are prepared by an alkoxylation reaction in which an alkylene oxide, such as ethylene oxide, is reacted under suitable conditions with an organic compound, such as an alcohol, having one or more active hydrogen atoms. In particular, ethylene oxide adducts of aliphatic alcohols or substituted phenols having from about 8 to 20 carbon atoms have found widespread utility as non-ionic detergent components or as intermediates for anionic detergent components of cleaning formulations for use in industrial and household applications.
Among the catalysts, potassium hydroxide (KOH) is the most widely used ethoxylation catalyst in the world. This is followed by sodium hydroxide (NaOH) and to an even lesser extent by sodium methylate (NaOMe). The ethoxylates produced using these catalysts are termed broad range ethoxylates (“BREs”) because they produce a broad range of alkoxylate species. See generally King, U.S. Pat. No. 5,114,900 and King, U.S. Pat. No. 5,120,697, which are incorporated by reference. These catalysts are generally used in the dry form or in an aqueous (except for NaOMe) or a methanolic medium. Prior to ethoxylation, in the case of dry catalyst, the water of reaction is removed by applying heat and vacuum or nitrogen sparge. Likewise, in the case of an aqueous or methanolic catalyst, the water or methanol is removed to generate the active catalyst prior to the start of ethoxylation of the substrate. Failure to do so results in ethoxylated by-products arising from side reactions with KOH, water or methanol.
In many instances, it is desirable to tailor the adduct number or ethoxymer distribution of a given product mixture to its intended service. For example, it is known that in surfactant applications, an adduct with too few ethylene oxide molecules is not effective because of poor water solubility. An adduct with too many ethylene oxide molecules is undesirable because surface tension reduction per unit mass decreases drastically with increasing hydrophilicity.
In order to meet this need, the prior art also contains catalysts to produce certain narrow range ethoxylates (“NRE”). For example, as taught in U.S. Pat. No. 4,239,917, which is incorporated by reference, it is desirable, particularly for surfactant applications, to use ethoxylates or alkoxylates with a narrow distribution in the desired mole adduct range of from about 2 to about 10 alkylene oxide adducts per alcohol molecule. The lower mole ethoxylates could serve as intermediates for anionic surfactants. Several references disclose the use of calcium-based catalysts for carrying out such alkoxylation reactions. See U.S. Pat. Nos. 4,754,075; 4,820,673; 4,835,321; 4,886,917; 5,220,046; 5,386,045; 5,627,121; and 6,147,246, all of which are incorporated by reference. As discussed in Lin, U.S. Pat. No. 5,627,121, these catalysts are often prepared in an alkoxylated alcohol mixture composed of alkoxylated alcohols and residual free alcohol. King, U.S. Pat. No. 5,114,900 discloses diols, such as ethylene glycol, propylene glycol, diethylene glycol, glycerol, butanediols, 1,3-propanediol, and the like as suitable dispersing media. However, the dispersing medium in these catalysts cannot be volatilized without losing a significant part of the substrate to be ethoxylated prior to ethoxylation. Consequently, the dispersing medium in the catalyst will end up being ethoxylated along with the substrate. This problem becomes even more pronounced in the case of producing higher mole ethoxylates where a higher level of the catalyst, relative to the substrate, is to be employed. This in turn will lead to correspondingly higher levels of by-products.
In sum, the prior art has taught the use of alcohol ethoxylates (Leach '321 Patent and Lin '121 Patent) or of diols or polyols (King '900 Patent) in the making of alkoxylation catalysts of high activity because of the high dispersing ability exerted by these solvents towards the calcium species. It is our surprising discovery that the use of simple short-chain alcohols and other dispersing media are effective in the production of highly active alkoxylation catalysts.